Field of the Disclosure
Embodiments disclosed herein relate generally to the use of threaded unions, particularly so-called “hammer unions,” and related methods of assembly.
Background Art
Threaded unions, particularly “hammer” unions, are commonly used in petroleum exploration and production to join conduits together, for example, conduits carrying high-pressure fluids such as drilling mud, fracturing fluids, and oil and gas produced incidental to drilling activities. Hammer unions are generally considered to be economical, simple, reliable, robust, and very easy to make-up and break-out quickly.
Typically, hammer unions are used more in temporary situations, such as joining together sections of joints (e.g., Chiksan® joints) used for pumping fracturing fluids into a wellbore under high pressure. Hammer unions may also be used in certain long-term applications for their ease of make-up and break-out, especially, for example, for equipment that may need to be replaced quickly and efficiently (e.g., rotary hoses for conveying drilling mud between a stand-pipe manifold and a rotary swivel or top drive, or components of a choke manifold, such as valves, chokes and spools, which may fail unexpectedly due to erosive flows).
Hammer unions typically include three major parts: a shouldered male sub, a threaded union nut, and a threaded female sub. The hammer union is typically made-up and broken-out by applying a sledge hammer to radial lugs on the threaded union nut. Referring now to FIG. 1, a cross-section view of a conventionally made-up hammer union with a spherical metal-to-metal pressure seal is shown. Threaded union nut 1 has hammer lugs 1A with internal threads 1B and flat surface 1C. Threaded union nut 1 bears on shoulder 2B on a distal end of shouldered male sub 2, which also has sealing surface 2C and outer diameter 5. Threaded female sub 3 has external threads 3A and sealing surface 3B.
Separation of hammer union connections under pressure due to metal fatigue is increasingly more common with increased flow rates and longer service lives. Fatigue fractures typically occur on the threaded union nut and female sub end, although they can occur in other regions as well. Accordingly, there exists a need for a hammer union connection that is more resistant to fatigue at higher flow rates and longer service life.